Proton Adducts Research Articles

A Comprehensive Report on the HPLC-ESI-MS/MS Method Development and Validation for Quantifying Cabotegravir in K3EDTA-Human Plasma, Employing Cabotegravir-D5 as an Internal Standard

Aiming to comprehend the plasma concentration of cabotegravir, a meticulously crafted bioanalytical method, aligned with the guidelines set by the US Food and Drug Administration (FDA), was devised and validated. This involved the utilization of cabotegravir D5 as an isotopic internal standard. The mobile phase consisted of methanol and 5 mM ammonium acetate in water, in an 80:20 ratio, v/v—Zorbax SB-C18 (50 × 2.1 mm, 5 μm) served as the chromatographic column. Cabotegravir and cabotegravir D5 were identified using proton adducts at m/z 409.20/370.20 and 409.20/144.8, respectively, employing the positive mode multiple reaction monitoring. Cabotegravir exhibited linearity within concentration ranges of 2 to 1000 ng/mL (r2 = 0.999). The recovery of cabotegravir from plasma by Liquid-liquid extraction yielded an average %CV of 7.71 at four quality control levels. Intra-day precision displayed accuracy of 100, 106, 97, 97, and 103%, respectively, whereas accuracy for inter-day precision was 100, 103, 98, 100, and 100% across LLQC, LQC, MQC-1, MQC-2, and HQC levels. The stability of cabotegravir remained consistent under diverse conditions, including five freeze-thaw cycles, benchtop, autosampler, and short-term, and long-term storage. This evaluation verifies that the method aligns with predefined acceptance limits and positions it as an indispensable tool in bioanalysis, significantly expanding its clinical utility.

Development and Validation of New LC-MS/MS Bioanalytical Method of Tremelimumab in Rat Plasma by Using Nivolumab as Internal Standard and Its Application with Pharmacokinetic Studies

Nivolumab was decided to be used as the IS. To separate the drugs, an isocratic mobile phase of acetonitrile (ACN): Ammonium formate containing formic acid (70:30) was adopted and delivered at 1-mL/min, along with a 150 x 4.6 mm x 3.5 μm Alliance, e2695 Luna Phenyl Hexyl column. Drug and IS, both of which display proton adducts approximately m/z 146.3685 to 120.0638 and m/z 143.7695 to 76.7964, might be detected simultaneously using MRM-positive modalities. Over a linearity level of 2.00 to 40.00 ng/mL, the method had a correlation value (r2) of 0.99977. The accuracy and precision of this method during the day ranged from 89.85 to 102.89% and 0.19 to 2.81%, respectively. Tremelimumab was reported to remain stable during three freeze-thaw cycles, benchtop tests, and postoperative stability studies. Cmax and Tmax values were acquired directly from experimental data. Cmax and Tmax averaged 18.024 ng/mL and 6 hours, respectively. At t1/2 of 18 hours, plasma levels began to fall. The obtained AUC024 and AUC0 values were 257 and 257 ng h/mL, respectively.

Cyclotribenzylene alkynylgold(I) phosphine complexes: synthesis, chirality, and exchange of phosphine.

Two different alkynyl-substituted C3-symmetric cyclotribenzylenes (CTB) were synthesized in racemic and enantiomerically pure forms, and six gold(I) phosphine complexes differing by the nature of the CTB and the phosphine were prepared and characterized, in particular by NMR spectroscopy, DOSY, electronic circular dichroism (ECD), and electrospray ionization mass spectrometry (ESI-MS). Their ECD patterns depended on the substitution of the starting CTBs and were shifted bathochromically by comparison with the latter. ESI-MS in the presence of HCO2H allowed us to detect the complexes as proton adducts. The intensities of the signals were stronger when the phosphine was more electron-rich. This technique was also used to investigate the exchange of phosphine betweeen pairs of CTB complexes. The scrambling reaction was demonstrated by the higher intensity of the signals of the complexes subjected to the exchange of a single phosphine ligand by comparison with the intensity of the signals of the starting complexes.

BIOANALYTICAL METHOD DEVELOPMENT AND VALIDATION OF MARALIXIBAT IN RAT PLASMA BY LC-MS/MS DETECTION AND ITS APPLICATION TO A PHARMACOKINETIC STUDY

Objective: To quantify maralixibat in rat plasma utilizing liquid-liquid extraction (LLE) approach, a practical, efficient, and accurate LC-MS/MS approach was devised. Methods: As an internal standard (IS), Elobixibat was adopted. Utilizing an Agilent eclipse C18, 150 mm x 4.6 mm, 3.5 µm column, the drug separation was accomplished using an isocratic mobile phase entailing acetonitrile (ACN) and buffer (1 ml Tri fluoro acetic acid into 1liter water and stir well. Filtered through 0.22µ membrane filter paper) composition of 70:30 (v/v), dispensed at 1.0 ml/min. Results: Multiple reaction monitoring (MRM) positive mode allowed for the simultaneous detection of maralixibat and elobixibat exhibiting proton adducts around m/z 676.0278-290.3625 and m/z 696.8541-480.6328, correspondingly. The correlation coefficient (r2) of the approach was ≥0.99977 across a linearity concentration spanning between 5.00–100.00 ng/ml. This technique achieved intra-day accuracy and precision between 99.31-100.93% and 0.22-6.55%, correspondingly. Across 3 freeze-thaw sessions, bench top testings, and postoperative stability investigations, maralixibat was shown to be stable. Conclusion: Through intravenous injection, this approach was effectively utilized in rats for studying the drug's pharmacokinetics.

Use of high-resolution mass spectrometry for the first-time identification of gerberin as a tentative marker of the fraudulent organic production of tomatoes

Solanum lycopersicum cv. Ramyle was cultivated using different amounts of synthetic and natural crop protection agents, combined with organic and chemical fertilisers. Chemometric studies on the LC-Q-Orbitrap metabolite profiles of tomatoes distinguished a compound [M+H]+ at m/z 291.1075 (C12H19O8+, 0.0 ppm). The compound, identified as gerberin, is a possible marker to distinguish between organic and conventional cultivation. To our knowledge, this is the first time gerberin has been identified in tomato. A combination of HRMS, in silico, and chemical experiments, allowed the structure elucidation. Target MS2 experiments of the 291.1075 peak showed a clear breakdown to a base peak at m/z 129.0546 Da, consistent with the gerberin aglycone proton adduct (C6H9O3). Acid hydrolysis of the extract showed the disappearance of all gerberin adducts remaining the 129.0546 ion only, which matched with a commercial standard of gerberin aglycone. The levels of gerberin in the samples correlated negatively with the presence of synthetic chemicals. Gerberin content variation correlated to the application of synthetic fertilisers (T1, T2, T3, and T4, from lowest to greatest application). δ15N IRMS measurements were insufficient to discern between agricultural practices, demonstrating that fraud in organic produce using synthetic fertilisers is possible if discrimination is based on IRMS only.

High throughput and very specific screening of anabolic-androgenic steroid adulterants in healthy foods based on stable isotope labelling and flow injection analysis-tandem mass spectrometry with simultaneous monitoring proton adduct ions and chloride adduct ions

In this work, a stable isotope labelling-flow injection analysis-tandem mass spectrometry (SIL-FIA-MS/MS) with simultaneous monitoring [M+H]+ and [M+Cl]− method was developed for very specific and high throughput screening of anabolic-androgenic steroids (AAS) illegally added to healthy foods. Initially, a simple centrifugation step was carried out for liquid samples, and for solid samples, a solid-liquid extraction step was conducted. Afterwards, batch chemical derivatization was carried out. After adding a certain amount of 13C6-3-NPH labelled AAS standards as the internal standards, it can be directly transferred for FIA-MS/MS analysis based on the no MS response characteristics of 3-NPH. The 3-NPH labelled AAS showed dual-polarity property, observing chloride adduct ion ([M+Cl]−) in negative ion mode and proton adduct ion ([M+H]+) in positive ion mode. The average time cost for pretreatment of each sample was less than 1 min by carrying out batch processing. The subsequent FIA-MS/MS detection enabled rapid and high throughput detection. The addition of 13C6-3-NPH-labelled AAS as internal standards can correct the matrix effect to achieve accurate quantitative analysis. The detection sensitivity was also improved by 2–5 folds after 3-NPH labelling. The limits of detection (LODs) in positive MRM mode were in ranges of 0.1–0.3 ng/mL. The validated method with simultaneous monitoring [M+H]+ and [M+Cl]− was validated in the range of 6.0–1000 ng/mL with the linear coefficient (R2) greater than 0.997. Satisfactory recoveries were found to be in ranges of 93.0–108.7%. The intra-day and inter-day RSDs were in the range of 3.5–9.9% and 5.1–14.1%, respectively. No changes in detection sensitivity of the mass spectrometry and no carry-over effects were found after numerous consecutive injections of AAS derivates. Compared with previously reported methods, the proposed method proved accurate, very specific, high throughput with good sensitivity.

Electrochemical reduction of CO2 to CO and HCOO- using metal-cyclam complex catalysts: predicting selectivity and limiting potential from DFT.

Sustainable fuel production from CO2 through electrocatalytic reduction is promising but challenging due to high overpotential and poor product selectivity. Herein, we computed the reaction free energies of electrocatalytic reduction of CO2 to CO and HCOO- using the density functional theory method and screened transition metal(M)-cyclam(L) complexes as molecular catalysts for CO2 reduction. Our results showed that pKa of the proton adduct formed by the protonation of the reduced metal center can be used as a descriptor to select the operating pH of the solution to steer the reaction toward either the CO or hydride cycle. Among the complexes, [LNi]2+ and [LPd]2+ catalyze the reactions by following the CO cycle and are the CO selective catalysts in the pH ranges 1.81-7.31 and 6.10 and higher, respectively. Among the complexes that catalyze the reactions by following the hydride cycle, [LMo]2+ and [LW]3+ are HCOO- selective catalysts and have low limiting potentials of -1.33 V and -1.54 V, respectively. Other complexes, including [LRh]2+, [LIr]2+, [LW]2+, [LCo]2+, and [LTc]2+ catalyze the reactions resulting in either HCOO- from CO2 reduction or H2 from proton reduction; however, HCOO- formation is always thermodynamically more favorable. Notably, [LMo]2+, [LW]3+, [LW]2+ and [LCo]2+ have limiting potentials less negative than -1.6 V and are based on Earth-abundant elements, making them attractive for practical application.

SENSITIVE BIO ANALYTICAL METHOD DEVELOPMENT AND VALIDATION OF VENETOCLAX IN HUMAN PLASMA BY LC-ESI-MS/MS

A specific and sensitive method of liquid chromatography–tandem mass spectrometry was demonstrated for the experimental determination of venetoclax in human plasma utilising venetoclax-D8 as an internal standard. The column Xbridge C18, 50 × 4.6mm, 5 µm was used for attaining chromatographic separation by utilising 10mM ammonium formate and methanol as isocratic mobile phase in the composition ratio of 20:80 (V/V). The flow-rate selected was 0.7ml/min. Venetoclax and venetoclax-D8 are identified in multiple reaction monitoring (MRM) positive mode with proton adducts at m/z 869.53 →553.21 and m/z 877.14 → 553.23, respectively. For the successful extraction of drug as well as internal standard, liquid-liquid extraction technique was efficiently utilised. The developed technique was established in a linear concentration range of 5.0-5000.0 pg/ml along with correlation coefficient (r2) of 0.9994. Intra and inter-day precisions were found to be 0.7 to 1.90% and 0.7 to 2.0 % for venetoclax and venetoclax-D8, respectively. Accuracy was found to be within 98.6 to 101.99% and 99.17 to 101.14 % for venetoclax and venetoclax-D8, respectively. It was observed that throughout the bench top studies, post-operative stability studies and freeze-thawing cycles, venetoclax retained stability.

A Novel Simultaneous Estimation of Sofosbuvir and Velpatasvir in Human Plasma by Liquid Chromatography Tandem-Mass Spectrometry after Protein Precipitation Method

Objective: The aim of the present work is to achieve a novel highly sensitive chromatographic method for the simultaneous determination of hepatitis C agents, sofosbuvir and velpatasvir from human plasma using ritonavir as an internal standard. Methods: Chromatographic separation was achieved using Hypersil C18 column (50mm x 4.6mm, 3μm) with an isocratic elution mode using the mobile phase composition 10 mM ammonium formate buffer (pH 5.0): acetonitrile (20:80 v/v) pumped at a flow rate of 0.5 ml/min. The detection was carried out by tandem mass spectrometry using Multiple Reaction Monitoring (MRM) positive Electrospray Ionization (ESI) with proton adducts at m/z 530.10 > 243.10, 883.40 > 114.0 and 721.25 > 197.0. Results: The method validated as per USFDA guidelines with respect to linearity, accuracy, and precision was found to be acceptable over the concentration range of 0.2–2000 ng/ml and 5-2000 ng/ml for sofosbuvir and velpatasvir respectively and the method was found to be highly sensitive and selective. Conclusion: The developed tandem mass spectrometric method is robust and can be applied for the monitoring of plasma levels of the analyzed drug in preclinical and clinical pharmacokinetic studies.

Development and Validation of An Analytical Liquid Chromatography-Tandem Mass Spectroscopy Method for the Estimation Febuxostat in Pharmaceutical Formulation

A rapid LC-MS/MS method has been developed and validated for the quantitative determination of Febuxostat from the commercially available formulations. The separation was achieved using Zorbax SB C18 column (4.6 × 50 mm, 5 μm) as a stationary phase and the mobile phase consists of (10 mM) Ammonium formate (pH4.0): methanol (10: 90 v/v) with a flow of 0.6 mL/min. Detection was carried out by triple quadrupole mass spectrometry with electrospray ionization in positive mode with proton adducts at m/z 316.95→260.95 to monitor Febuxostat within a run time of 2 min. The linearity of the method was found over a concentration range of 4 to 55 ng/mL with a regression analysis of 0.997. The percentage recovery of the present method was found to be 97.16 to 99.46%. The LC-MS/MS method was validated as per ICH guidelines. The developed method can be successfully applied for the estimation of Febuxostat in the commercial formulation and in bulk drug.

Simultaneous Quantification of Pantoprazole and Levosulpiride in Spiked Human Plasma Using High Performance Liquid Chromatography Tandem Mass Spectrometry

Background: Pantoprazole (PTZ) and Levosulpiride (LS) were proven as effective agents for the treatment of Gastro-Esophageal Reflux Disease (GERD). It is a complex motor disorder that results in regurgitation of the gastric contents into the lower esophagus with consequent symptoms such as heart burn, retrosternal pain, dysphagia and belching. Methods: A rapid, sensitive, selective and specific liquid chromatography- electro spray ionization tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous quantification of Pantoprazole (PTZ) and Levosulpiride (LS) in spiked Human Plasma. The method utilized SPE as sample preparation technique and the analysis was carried out on a HPLC system utilizing electro spray ionization as interface and triple quadrupole mass analyzer for quantification in MRM possitive mode. Iloperidone was used as internal standard (IS). Chromatographic separation was performed on a Phenomenex C-18 Column (4.6 mm x 50 mm, 5µ) with an isocratic elution mode utilizing a mobile phase composition of Solution containing a mixture of 70 volumes of acetonitrile: 30 volumes of methanol and 10mM ammonium formate (pH 4.0) at the ratio of 80:20 % v/v. The flow rate was maintained at 0.3 mL/min. Results: PTZ, LS and IS were detected and quantified with proton adducts at m/z 383.37→200.00, m/z 341.42→112.15 and 426.48→261.00 respectively. The linearity and range was established by fortifying blank plasma samples in the concentration range of 3.5-2000 ng/mL for PTZ and 3.0-2400 ng/mL for LS. The correlation coefficient (r2) was found to be ≥ 0.993 for PTZ and (r2) ≥ 0.990 for LS. The lower limit of quantification for PTZ was 3.5 ng/mL and LS was 3.0 ng/mL. The intra and inter day precision and accuracy for PTZ and LS were within the limits fulfilling the international acceptance criteria. PTZ and LS were found to be stable throughout three freeze-thaw cycles, bench top and short term stability studies. Conclusion: The proposed validated LC-MS/MS method offers a sensitive quantification of PTZ and LS in spiked human plasma and can be utilized for the quantification of PTZ and LS in real-time samples.

Evaluation of Deuterium-Labeled Internal Standard for the Measurement of Venetoclax by HPLC-ESI -Tandem Mass Spectrometry

<p style="text-align: justify;"><strong>Objective:</strong> Venetoclax is a selective, potent, first-in-class BCL-2 inhibitor that restores apoptosis in cancer cells and has demonstrated clinical efficacy in a variety of haematological malignancies. There is no reported evidence for its measurement in human plasma. <strong>Method:</strong> A simple, sensitive and specific high-throughput HPLC-ESI-Tandem Mass Spectrometric method was developed for the estimation of Venetoclax (VX) in human plasma using Venetoclax-D8 (VXD8) as an internal standard (IS). Chromatographic separation was performed on Zorbax SB-C18, 75 x 4.6 mm, 3.5 mm, 80 &Aring; column with an isocratic mobile phase composed of Methanol and 5mM Ammonium acetate in the ratio of (70:30 v/v), at a flow-rate of 0.6 mL/min. The proton adducts of VX and VXD8 were detected at m/z 868.12 &rarr; 321.54 and 876.9 &rarr; 329.7 respectively, using multiple reaction monitoring (MRM) positive mode respectively. The Liquid-Liquid extraction method was used to extract the analyte and IS. <strong>Results:</strong> The method was successfully validated over linearity concentration range of 10.0-10000.0 pg/mL with the correlation coefficient (r²) &ge; 0.9997. This method demonstrated intra and inter-day precision within 5.7 to 7.7 and 5.95 to 8.5 and % Accuracy within 96.3 to 98.7 and 98 to 100.4 %. Venetoclax was found to be stable throughout freeze-thawing cycles, bench top, postoperative stability studies. <strong>Conclusion:</strong> The method was suitable and conveniently applicable to pharmacokinetic and bioavailability studies for estimation of Venetoclax in biological matrices by HPLC-MS/MS. <p style="text-align: justify;"><strong>Key words:</strong> Deuterium, Pharmacokinetic, Plasma, Proton adduct, Venetoclax.

A sensitive bioanalytical method development and validation of cabozantinib in human plasma by LC-ESI-MS/MS

ABSTRACT A simple, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of cabozantinib (CZ) in human plasma using cabozantinib-d4 (CZD4) as an internal standard (IS). Chromatographic separation was performed on Xbridge C18, 50 x 4.6 mm, 5 mm column with an isocratic mobile phase composed of 10mM Ammonium formate and Methanol in the ratio of (20:80 v/v), at a flow-rate of 0.7 mL/min. CZ and CZD4 were detected with proton adducts at m/z 502.2 ® 391.1 and 506.3 ® 391.2 in multiple reaction monitoring (MRM) positive mode respectively. Liquid-Liquid extraction method was used to extract the drug and IS. The method was validated over a linear concentration range of 5.0-5000.0 pg/mL with correlation coefficient (r2) ≥ 0.9994. This method demonstrated intra and inter-day precision within 1.95 to 2.37 and 2.93 to 9.3 % and Accuracy within 101.4 to 102.4 and 99.5 to 104.8 %. Cabozantinib was found to be stable throughout freeze-thawing cycles, bench top and postoperative stability studies.

Laser Desorption/Ionisation Mass Spectrometry Imaging of European Yew (Taxus baccata) on Gold Nanoparticle-enhanced Target.

European yew (Taxus baccata) is a plant known to man for centuries as it produces many interesting and important metabolites. These chemical compounds were repeatedly analysed by various analytical techniques, but none of the methods used so far allowed the localisation of the chemical compounds within the tissue and also correlation between plant morphology and its biochemistry. Visualisation of the spatial distribution of yew metabolites with nanoparticle-based mass spectrometry imaging. Compounds occurring on cross-section of a one-year yew sprig has been transferred to gold nanoparticle-enhanced target (AuNPET) by imprinting. The imprint was then subjected to mass spectrometry imaging analysis. Nanoparticle-enhanced mass spectrometry imaging made it possible to study the distribution of selected compounds in the European yew tissue, including taxanes - terpene alkaloids characteristic for the Taxus genus. Results prove that aspartate, taxinine M, baccatin IV and taxine B are located mainly in the cortex. Taxuspine W was located in the vascular tissue. Maleate was found to be located mainly in the phloem tissue. In contrast, the proton adduct of chlorophyll b was found in the external layer of twigs. The results presented a high correlation between the location of compounds and the morphology of the plant, thus giving the opportunity to see the selected details of chemical structure of the analysed tissue for the first time. Copyright © 2017 John Wiley & Sons, Ltd.

Nitrogen oxides as dopants for the detection of aromatic compounds with ion mobility spectrometry

Limits of detection (LODs) in ion mobility spectrometry (IMS) strictly depend on ionization of the analyte. Especially challenging is ionization of compounds with relatively low proton affinity (PA) such as aromatic compounds. To change the course of ion-molecule reactions and enhance the performance of the IMS spectrometer, substances called dopants are introduced into the carrier gas. In this work, we present the results of studies of detection using nitrogen oxides (NOx) dopants. Three aromatic compounds, benzene, toluene, toluene diisocyanate and, for comparison, two compounds with high PA, dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP), were selected as analytes. The influence of water vapour on these analyses was also studied. Experiments were carried out with a generator of gas mixtures that allowed for the simultaneous introduction of three substances into the carrier gas. The experiments showed that the use of NOx dopants significantly decreases LODs for aromatic compounds and does not affect the detection of compounds with high PA. The water vapour significantly disturbs the detection of aromatic compounds; however, doping with NOx allows to reduce the effect of humidity.Graphical Two possible ionization mechanisms of aromatic compounds in ion mobility spectrometry: proton transfer reaction and adduct formation

Peculiarities of data interpretation upon direct tissue analysis by Fourier transform ion cyclotron resonance mass spectrometry.

The importance of high-resolution mass spectrometry for the correct data interpretation of a direct tissue analysis is demonstrated with an example of its clinical application for an endometriosis study. Multivariate analysis of the data discovers lipid species differentially expressed in different tissues under investigation. High-resolution mass spectrometry allows unambiguous separation of peaks with close masses that correspond to proton and sodium adducts of phosphatidylcholines and to phosphatidylcholines differing in double bond number.

Novel LC- ESI-MS/MS method for desvenlafaxine estimation human plasma: application to pharmacokinetic study.

A simple, sensitive and specific liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) method was developed for the quantification of desvenlafaxine in human plasma using desvenlafaxine d6 as an internal standard (IS). Chromatographic separation was performed using a Thermo-BDS hypersil C8 column (50 × 4.6 mm, 3 µm) with an isocratic mobile phase composed of 5 mM ammonium acetate buffer: methanol (20:80, v/v), at a flow rate of 0.80 mL/min. Desvenlafaxine and desvenlafaxine d6 were detected with proton adducts at m/z 264.2/58.1 and 270.2/ 64.1 in multiple reaction monitoring positive mode, respectively. Liquid-liquid extraction was used to extract the drug and the IS. The method was linear over the concentration range 1.001-400.352 ng/mL with a correlation coefficient of ≥0.9994. This method demonstrated intra and inter-day precision within 0.7-5.5 and 1.9-6.8%, and accuracy within 95.3-107.4 and 93.4-99.5%. Desvenlafaxine was found to be stable throughout the freeze-thaw cycles, bench-top and long-term matrix stability studies. The developed and validated method can be successfully applied for the bioequivalence/pharmacokinetic studies of desvenlafaxine in pharmaceutical dosage forms.

Identification of isobaric lyso-phosphatidylcholines in lipid extracts of gilthead sea bream (Sparus aurata) fillets by hydrophilic interaction liquid chromatography coupled to high-resolution Fourier-transform mass spectrometry.

The numerous and varied biological roles of phosphatidylcholines (PC) and lysophosphatidylcholines (LPC) have fueled a great demand for technologies that enable rapid, in-depth structural examination of these lipids in foodstuffs. Here, we describe the capabilities of a newly configured combination of high-efficiency liquid chromatography and high-resolution/accuracy Fourier-transform mass spectrometry with electrospray ionization (LC-ESI-FTMS), designed for lipidomics applications that require the identification of PC in their lyso forms. The devised strategy, involving a separation by hydrophilic interaction liquid chromatography (HILIC) on spherical, fused-core ultrapure silica particles (2.7μm) of a narrow-bore column (2.1mm i.d.), enabled the identification of as many as 71 LPC species in the lipid extracts of gilthead sea bream (Sparus aurata) fillets. In this way, LPC as proton (43) and sodium (28) adducts, i.e., [M + H](+) and [M + Na](+) ions (with M representing the zwitterionic form), were identified. In several cases, the extremely high (sub-ppm) mass accuracy and the high chromatographic efficiency available with the adopted instrumentation enabled the distinction of isobaric and closely eluting LPC species. Informative tandem mass spectra, based on high-energy collision induced dissociation (HCD), were also obtained, thus distinguishing regioisomeric LPC species (i.e., LPC differing only for the location of the residual side chain on the glycerol backbone) and between proton and sodium adducts. Graphical Abstract Extracted Ion Current chromatogram (XIC) obtained for the m/z value 568.339, showing the presence of two regioisomeric Lysophosphatidylcholines. The corresponding high collisional energy tandem MS spectra, obtained using a HCD cell, are shown as insets.

Development and Validation of LC-MS/MS Method for Determination of Trimipramine Maleate in Human Plasma

A simple, sensitive, Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) method was developed for the determination of Trimipramine maleate in human plasma using Opipramol dihydrochloride as internal standard (ISTD). The analyte and ISTD were isolated from plasma by protein precipitation method using methanol. The chromatographic separation was carried out on ZORBAX ECLIPSE XDB- C18 column (4.6 x 150 mm, 5 µm). The elution was done with isocratic mobile phase composed of 5mM ammonium formate with 0.1% formic acid and methanol in the ratio of 25:75(v/v) at a flow rate of 1.0 ml/min. Trimipramine and Opipramol were detected with proton adducts at m/z 295.20→100.10 and m/z 364.30→171.20 in multiple reaction monitoring (MRM) positive mode respectively. The retention time of Trimipramine and ISTD were found to be 1.67min and 1.48min respectively. The calibration curves were linear over concentration range of 0.1 to 100.1 ng/ml. The lower limit of quantification was found to be 0.1 ng/ml. The method was validated by EMEA (European medicines agency) guidelines for linearity, accuracy & precision, matrix factor, recovery, selectivity and stability. The validation parameters were found to be well within the acceptance limit.

Inverse kinetic solvent isotope effect in TiO2 photocatalytic dehalogenation of non-adsorbable aromatic halides: a proton-induced pathway.

An efficient redox reaction between organic substrates in solution and photoinduced h(+) vb /e(-) cb on the surface of photocatalysts requires the substrates or solvent to be adsorbed onto the surface, and is consequentially marked by a normal kinetic solvent isotope effect (KSIE ≥ 1). Reported herein is a universal inverse KSIE (0.6-0.8 at 298 K) for the reductive dehalogenation of aromatic halides which cannot adsorb onto TiO2 in a [D0 ]methanol/[D4 ]methanol solution. Combined with in situ ATR-FTIR spectroscopy investigations, a previously unknown pathway for the transformation of these aromatic halides in TiO2 photocatalysis was identified: a proton adduct intermediate, induced by released H(+) /D(+) from solvent oxidation, accompanies a change in hybridization from sp(2) to sp(3) at a carbon atom of the aromatic halides. The protonation event leads these aromatic halides to adsorb onto the TiO2 surface and an ET reaction to form dehalogenated products follows.